The present invention relates to device select systems, and more particularly, this invention relates to a device select system and methods for selecting devices on multiple magnetic heads.
Business, science and entertainment applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 512 or more data tracks.
The improvement in magnetic medium data storage capacity arises in large part from improvements in the magnetic head assembly used for reading and writing data on the magnetic storage medium. A major improvement in transducer technology arrived with the magnetoresistive (MR) sensor originally developed by the IBM® Corporation. Later sensors using the GMR effect were developed. AMR and GMR sensors transduce magnetic field changes to resistance changes, which are processed to provide digital signals. Data storage density can be increased because AMR and GMR sensors offer signal levels higher than those available from conventional inductive read heads for a given read sensor width and so enable smaller reader widths and thus more tracks per inch. Moreover, the sensor output signal depends only on the instantaneous magnetic field intensity in the storage medium and is independent of the magnetic field time-rate-of-change arising from relative sensor/medium velocity. In operation the magnetic storage medium, such as tape or a magnetic disk surface, is passed over the magnetic read/write (R/W) head assembly for reading data therefrom and writing data thereto.
However, increased storage capacity does not come without cost. For instance, as the number of R/W elements on a given head increases, so too must the number of electrical connections to the head. This means that the cable(s) connecting the head to the controller must accommodate the increased number of connections. One problem that arises is that cables tend to get more complex and costly as the number of devices in the head, and therefore the number of leads in the cable, increases. Further, cables tend to get wider, and thus stiffer and more massive as the number of leads increases, which in turn can negatively affect actuator bandwidth and make cable routing for freedom of motion more difficult. Generally, shrinking the dimensions of the leads in the cable is not an option, as DC resistance and AC impedance would also change undesirably.
Current technology fails to address tape head cabling problems that will be posed by bourgeoning I/O needs for future multi-track, multi-format or multi-function tape heads.